A typical heat exchanger comprises a plurality of parallel, spaced apart fins defining air flow passages. The fins are typically made of aluminum and aluminum alloys due to the excellent heat conductance properties of aluminum. The heat exchanger fins are designed to have surface areas which are as large as possible, and spaces between the fins which are as narrow as possible without increasing the resistance to air flow between the fins, in order to increase the heat radiation or cooling effect.
As a result, particularly when the heat exchanger is used for cooling, moisture from warm air passing through the heat exchanger condenses on the cold fin surfaces and, if those surfaces are hydrophobic, beads of water accumulate to block the narrow passages between adjacent heat exchanger fins. The increased resistance to air flow operates to reduce the efficiency of the heat exchangers.
In order to help prevent the accumulation of water between heat exchanger fins, the surfaces of the heat exchanger fins have been coated with hydrophilic coatings so that a thin film of water coating the surface can readily slide off the surface of the heat exchanger fins, a phenomenon known as "sheeting off", to prevent blockage of the narrow passages between the adjacent heat exchanger fins.
The hydrophilic coatings which have been employed to date have included chromates and silicates. These hydrophilic coatings have some undesirable characteristics which include, being toxic, producing an unpleasant odor, and having relatively weak corrosion resistance due to relatively poor adhesion to surfaces and high surface coating porosity which can allow corrosive materials to permeate and react with metal surfaces.
Accordingly, it would be desirable to provide a hydrophilic coating composition which produces coatings which are non-toxic, do not produce an unpleasant odor and have improved corrosion resistance.
Also, the coatings should be less than, or equal to, about 5 microns, uniform and essentially free of gaps and/or holes. Thus, it would be desirable to provide coatings which are thin, uniform and essentially free of gaps and/or holes.